I just wanted to know what the characteristics are for the sound/letter produced in the ishmaam of the zay and the saad.
Jazkallahu khair

I just wanted to know what the characteristics are for the sound/letter produced in the ishmaam of the zay and the saad. Does it lose/gain any characteristics as the saad/zay goes to this letter?

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh
This kind of ishmaam, which means mixing of sounds, occurs in the qira'aat, not in the recitation of Hafs. There are some cases in which the letter is pronounced with a mix (ishmaam) of the and the letter . With this, the letter is pronounced with the jahr of the letter , but the and of the . It therefore sounds like a with tafkheem and compression of the sound (iTbaq).